1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine.
2. Description of the Related Art
In a conventional image forming apparatus, as an image bearing member receives a discharge from a charging member, a discharge product attaches to a surface of the image bearing member, and endurance gradually raises a frictional force between the image bearing member and a cleaning blade. When the frictional force between the image bearing member and the cleaning blade increases, followability of the cleaning blade with respect to the image bearing member becomes unstable, causing a chattering phenomenon in which the cleaning blade bounces or causing a turning-over phenomenon in which the cleaning blade is reversed. Thereby, the amount of toner slipping through increases and image defects are caused.
Therefore, a method has been proposed which reduces the frictional force by developing a belt-shaped toner belt and sending toner between the image bearing member and the cleaning blade. Japanese Patent Laid-Open no. 2005-250215 (Patent literature 1) proposes a method of changing an imaging frequency of a toner belt according to use history of a cleaning blade and an image bearing member. Also, Japanese Patent laid-Open no. 2006-139111 (Patent literature 2) proposes a method of forming a toner belt when an image area ratio is equal to or less than a predetermined level.
However, even when toner supply is performed as described above, an abrupt change of the frictional force between the image bearing member and the cleaning blade during a printing operation can change driving load torque (dynamic torque) of the image bearing member.
FIGS. 12A and 12B are diagrams illustrating an abutting state of an image bearing member and a cleaning blade. FIG. 12A illustrates a state in which a frictional force between the image bearing member and the cleaning blade is high, and FIG. 12B illustrates a state in which the frictional force is low. In the state of FIG. 12A, the abutting portion of the cleaning blade is drawn in a downstream side to a large extent from an abutting position while being stopped. In the state of FIG. 12B, the downstream-side drawing-in amount of the abutting portion of the cleaning blade is smaller as compared with FIG. 12A.
An abrupt change of blade behavior forces toner, which has accumulated near the cleaning blade, to slip through little by little from contact portions of the cleaning blade and the image bearing member. The toner that has slipped through contaminates the surface of the charging member, which lies downstream in the rotation direction of the image bearing member, and causes local latent image unevenness, or the toner is transferred onto a sheet and results in image defects.
In this regard, a method is also considered which supplies the cleaning blade with fog toner by rotating a development sleeve at a low speed during a non image forming time, in order to suppress any abrupt change of blade behavior when switching from the non image forming time to an image forming time. However, there is a concern that the developer will degrade as much as the development sleeve is rotated.